Assessment of QT interval and QT dispersion for prediction of all-cause and cardiovascular mortality in American Indians: The Strong Heart Study

Prolonged QTc interval and risk of sudden cardiac death in a population of older adults

OBJECTIVES

This study sought to investigate whether prolongation of the heart rate-corrected QT (QTc) interval is a risk factor for sudden cardiac death in the general population.

BACKGROUND

In developed countries, sudden cardiac death is a major cause of cardiovascular mortality. Prolongation of the QTc interval has been associated with ventricular arrhythmias, but in most population-based studies no consistent association was found between QTc prolongation and total or cardiovascular mortality. Only very few of these studies specifically addressed sudden cardiac death.

METHODS

This study was conducted as part of the Rotterdam Study, a prospective population-based cohort study that comprises 3,105 men and 4,878 women aged 55 years and older. The QTc interval on the electrocardiogram was determined during the baseline visit (1990 to 1993) and the first follow-up examination (1993 to 1995). The association between a prolonged QTc interval and sudden cardiac death was estimated using Cox proportional hazards analysis.

RESULTS

During an average follow-up period of 6.7 years (standard deviation, 2.3 years) 125 patients died of sudden cardiac death. An abnormally prolonged QTc interval (>450 ms in men, >470 ms in women) was associated with a three-fold increased risk of sudden cardiac death (hazard ratio, 2.5; 95% confidence interval, 1.3 to 4.7), after adjustment for age, gender, body mass index, hypertension, cholesterol/high-density lipoprotein ratio, diabetes mellitus, myocardial infarction, heart failure, and heart rate. In patients with an age below the median of 68 years, the corresponding relative risk was 8.0 (95% confidence interval 2.1 to 31.3).

CONCLUSIONS

Abnormal QTc prolongation on the electrocardiogram should be viewed as an independent risk factor for sudden cardiac death.

Coronary heart disease risk equivalence in diabetes depends on concomitant risk factors

OBJECTIVE

Diabetes has been defined as a coronary heart disease (CHD) risk equivalent, and more aggressive treatment goals have been proposed for diabetic patients.

RESEARCH DESIGN AND METHODS

We studied the influence of single and multiple risk factors on the 10-year cumulative incidence of fatal and nonfatal CHD and cardiovascular disease (CVD) in diabetic and nondiabetic men and women, with and without baseline CHD or CVD, in a population (n = 4,549) with a high prevalence of diabetes.

RESULTS

In both sexes, diabetes increased the risk for CHD (hazard ratio 1.99 and 2.93 for men and women, respectively). Diabetic men and women had a 10-year cumulative incidence of CHD of 25.9 and 19.1%, respectively, compared with 57.4 and 58.4% for nondiabetic men and women with previous CHD. The pattern was similar when only fatal events were considered. Diabetic individuals with one or two risk factors had a 10-year cumulative incidence of CHD that was only 1.4 times higher than that of nondiabetic individuals (14%). However, the 10-year incidence of CHD in diabetic subjects with multiple risk factors was >40%, and the incidence of fatal CHD was higher in these subjects than in nondiabetic subjects with previous CHD. Data for CVD showed similar patterns, as did separate analyses by sex.

CONCLUSIONS

Our results and comparisons with other available data show wide variation in the rate of CHD in diabetes, depending on the population and existing risk factors. Most individuals had a 10-year cumulative incidence >20%, but only those with multiple risk factors had a 10-year cumulative incidence that was equivalent to that of patients with CHD. Until more data are available, it may be prudent to consider targets based on the entire risk factor profile rather than just the presence of diabetes.

Long-term prognostic value of the preoperative 12-lead electrocardiogram before major noncardiac surgery in coronary artery disease

BACKGROUND

Knowledge of the prognostic information of preoperative 12-lead electrocardiogram (ECG) recordings in patients with coronary artery disease (CAD) undergoing noncardiac surgery is limited.

METHODS

The prognostic information derived from the preoperative ECGs of 172 CAD patients undergoing major noncardiac surgery was analyzed to determine its predictive value for long-term outcome. Primary end point was all-cause mortality; secondary end point was major adverse cardiac events (MACE) at 2 years.

RESULTS

Prevalence of ECG abnormalities was 53% for T-wave alterations; 46% for Q waves; 38% for ST deviations; and, depending on the criterion used, 2% to 19% for left ventricular hypertrophy. During follow-up, 40 (23%) patients died and 31 (18%) had MACE. After adjustment for clinical baseline findings, including current medication with beta-blockers, ST depressions (odds ratio [OR] 4.5, 95% confidence interval [CI] 1.9-10.5) and faster heart rate (HR) (OR 1.6, 95% CI 1.1-2.4, per 10 beats per minute [bpm] increase) were independent predictors of all-cause mortality. Faster HR (OR 1.7, 95% CI 1.1-2.6, per 10-bpm increase) was also an independent predictor of MACE. The predictive value of ECG variables did not change after adjustment for occurence of perioperative ischemia.

CONCLUSION

In CAD patients, the preoperative ECG contains important prognostic information and is predictive of long-term outcome independent of clinical findings and perioperative ischemia.

Increased QT dispersion: a negative prognostic finding in chronic obstructive pulmonary disease

OBJECTIVE

Chronic obstructive pulmonary disease (COPD) is a highly prevalent syndrome, deeply affecting the cardiovascular system as well as the lungs. We investigated the prognostic role of the QT interval and QT dispersion (QTD) in predicting all-cause, respiratory and cardiovascular mortality in COPD, and the relationship between these electrocardiographic parameters and pulmonary function in a prospective longitudinal study.

METHODS

We studied 246 COPD patients without significant co-morbidities, with a mild to moderate functional impairment, admitted to the Department of Internal Medicine from January 1995 to December 2001, performing a 5-year mean follow-up (5-116 months) up to August 2004. After clinical stabilisation, an electrocardiogram and functional respiratory tests were obtained, allowing measurement of the QT interval and QTD, forced vital capacity (FVC), forced expiratory volume at 1 s (FEV1), inspiratory capacity, FEV1/FVC ratio, partial oxygen pressure and partial carbon dioxide pressure in arterial blood.

RESULTS

At the end of the follow-up period, 81 patients were dead, 165 still alive; 36 died because of respiratory causes, 23 because of cardio-cerebrovascular events, 21 because of cancer (mainly lung cancer). A significant high incidence of sudden cardiac death was observed. QTD and QTcD showed a significant relationship with respiratory functional parameters. Maximal QT interval, QTcD and QTD appear to be independent predictors of all-cause, cardiovascular and respiratory mortality (relative risk 1.94, 3.22, 2.88, respectively). Age > 65 years, partial oxygen pressure < 60 mmHg and inspiratory capacity < 80% of the predicted value were the only other independent predictive parameters.

CONCLUSIONS

Maximal QT interval, QTD and QTcD are independent predictors of mortality. A significant incidence of cardiac sudden death was observed. These findings suggest the need for a global and multidisciplinary risk assessment in COPD patients. Intriguing relationships between the QTD and functional respiratory parameters were also observed.

QT dispersion in sarcoidosis

STUDY OBJECTIVES

QT dispersion (QTd) is the maximal interlead difference in QT interval on surface 12-lead ECG. An increase in QTd is found in various cardiac diseases. Sarcoidosis augments inhomogeneity in ventricular repolarization by sarcoid granuloma, which significantly correlates with ventricular fibrillation. Changes in QTd in the course of sarcoidosis have not been investigated previously.

DESIGN

The study included 35 patients with systemic sarcoidosis. The diagnosis of systemic sarcoidosis was made by biopsy. Thallium scintigraphy was performed in all patients with systemic sarcoidosis. Cardiac sarcoidosis was diagnosed in 16 patients based on abnormal thallium scintigraphy and normal coronary arteriography results. QTd, corrected QTd (cQTd), maximum QT (QTmax), maximum corrected QT (cQTmax), minimum QT, and minimum corrected QT intervals were measured. Twenty-four healthy subjects represented the control group for QT interval analysis.

MEASUREMENTS AND RESULTS

In the cardiac sarcoidosis group, mean QTd (+/- SD) was significantly greater than in the noncardiac sarcoidosis group and control group (49.50 +/- 10.86 ms, 28.14 +/- 11.02 ms, and 27.08 +/- 10.41 ms, respectively; p < 0.001). cQTd was significantly greater in the cardiac sarcoidosis group than in the noncardiac sarcoidosis group and control group (53.17 +/- 10.44 ms, 30.61 +/- 10.94 ms, and 29.01 +/- 10.52 ms, respectively; p < 0.001). QTmax (440 +/- 15.01 ms, 409 +/- 14.86 ms, and 410 +/- 13.21 ms; p < 0.001) and cQTmax (449 +/- 16.31 ms, 417 +/- 12.51 ms, and 418 +/- 11.76, respectively; p < 0.001) were also significantly greater in patients with cardiac sarcoidosis. In a limited follow-up group (11 cardiac and 9 noncardiac sarcoidosis patients), the incidence of premature ventricular contraction (PVC) on ECG was greater in the cardiac sarcoidosis group than in the noncardiac sarcoidosis group (36% and 0%, respectively; p < 0.05). A medium correlation existed between QTd and PVC (r = 0.331, p < 0.05).

CONCLUSIONS

QTd, cQTd, QTmax, and cQTmax are prolonged in patients with cardiac sarcoidosis compared to the patients with noncardiac sarcoidosis and control subjects. The incidence of PVC on ECG was greater in the cardiac sarcoidosis group than in the noncardiac sarcoidosis group.

Repolarization Abnormality for Prediction of All-Cause and Cardiovascular Mortality in American Indians: The Strong Heart Study

BACKGROUND

Analysis of electrocardiographic (ECG) repolarization abnormality using QTc interval and principal component analysis (PCA) of the T-wave vector predict all-cause and cardiovascular (CV) mortality. Novel descriptors of T-wave morphology have been suggested as measures of repolarization heterogeneity and adverse prognosis. However, whether these T-wave descriptors provide prognostic information beyond QTc and the PCA ratio has not been examined.

METHODS AND RESULTS

Predictive values of QTc, PCA, and novel ECG variables characterizing the T-wave loop were assessed in 1,729 American Indian participants in the first Strong Heart Study exam. T-loop morphology was quantified by the ratio of the second to first eigenvalues of the T-wave vector (PCA ratio), T-loop area (TLA) projected onto the dominant vector plane, T-wave morphology dispersion (TMD) and by the sum of the squares of the fourth to eighth eigenvalues, the T-wave residuum (TWR). After mean follow-up of 4.8 +/- 0.8 years, there were 183 deaths from all causes, including 51 CV deaths. In univariate Cox analyses, prolonged QTc, increased PCA ratio, TLA, TMD, and TWR were significant predictors of all-cause and CV mortality (P < 0.001). In multivariate Cox analyses adjusting for demographic and clinical risk factors for mortality, increased PCA ratio (chi-square = 7.9, P = 0.005) and TWR (chi-square = 5.3, P = 0.022) remained significant predictors of CV mortality and increased QTc (chi-square = 12.1, P < 0.001) and TWR (chi-square = 6.0, P = 0.014) of all-cause mortality. Addition of TWR to the model with clinical variables and the PCA ratio for CV mortality and to the model with clinical variables and prolonged QTc for all-cause mortality increased prognostic value of each model (increase in overall chi-square from 287.5 to 301.9 and from 221.5 to 230.3, respectively).

CONCLUSION

Novel descriptors of T-wave complexity provide additional prognostic information beyond QTc and PCA ratio for prediction of all-cause and CV mortality.

A genetic and epidemiologic study of cardiovascular disease in Alaska natives (GOCADAN): design and methods

This article is a report of the design and methods of the Genetics of Coronary Artery Disease in Alaska Natives (GOCADAN) Study. This longitudinal, population-based study was initiated to investigate the genetic determinants of cardiovascular disease and its risk factors. Between October 2000 and April 2004, this family study enrolled 1,214 Eskimos from several coastal villages in the Norton Sound region of Western Alaska. Examinations included a physical, laboratory determinations, and measures of subclinical disease. This study will generate a genome-wide scan for loci influencing cardiovascular disease-related traits. Relations between subclinical atherosclerosis and markers of inflammation will be examined using historic and newly drawn samples. The study will provide data on CVD prevalence, risk factors and the relative contribution of genetic and environmental determinants in Alaska Native peoples. Data from this study will contribute to the delivery of health-care and prevention of CVD in Alaska Eskimos and other populations.

Comparison of the four formulas of adjusting QT interval for the heart rate in the middle-aged healthy Turkish men

OBJECTIVE

The aim of this study was to evaluate the QT intervals at different rest heart rates in healthy middle-aged Turkish men and to compare the known four QT adjusting methods for heart rate.

METHODS AND RESULTS

The QT intervals were measured in electrocardiograms of 210 healthy men (mean age = 35-60 years). A curve relating QT intervals and heart rates from 45 to 135 beats/min was constructed for study population. Based on the formula of Bazett, Fridericia, and Framingham, adjusted QT intervals in these range of heart rates were separately estimated. An adjusting nomogram for different heart rates was created using a reference value, which was the measured QT interval at heart rate of 60 beats/min (QT(No) = QT + correcting number). These four QT correction methods were compared with each other. The reference value of QT interval at heart rate of 60 beats/min was 382 ms. The relationship between QT and RR interval was linear (r = 0.66, P < 0.001). Nomogram method corrected QT interval most accurately for all the heart rates compared with other three adjusting methods. At heart rates of 60-100 beats/min, the equation of linear regression was QT = 237 + 0.158 x RR (P < 0.001). Bazett's formula gave the poorest results at all the heart rates. The formulas of Fridericia and Framingham were superior to Bazett's formula; however, they overestimated QT interval at heart rate of 60-110 beats/min (P < 0.01). At lower rates (<60 beats/min), all methods except nomogram method, underestimated QT interval (P = 0.03).

CONCLUSION

Among four QT correction formulas, the nomogram method provides the most accurately adjusted values of QT interval for all the heart rates in healthy men. Bazett's formula fails to adjust the QT interval for all the heart rates.

Action Potential Duration and QT Interval During Pinacidil Infusion in Isolated Rabbit Hearts

INTRODUCTION

Acute myocardial ischemia, which opens K(ATP) channel, is associated with shortened action potential duration (APD) but prolonged QT interval. This discrepancy has not been adequately explained. We hypothesize that the duration of intracellular calcium (Ca(i)) transient (DCaT) may play a role in determining QT interval.

METHODS AND RESULTS

We performed simultaneous optical mapping of voltage and Ca(i) in 15 isolated rabbit hearts during a K(ATP) channel opener (pinacidil) infusion. Anterior epicardial mapping (n = 7) showed no difference of APD(90), QT interval, and the DCaT(90) at baseline. When perfused with 80 microM pinacidil, the APD(90), the QT interval, and the DCaT(90) were 105 +/- 10 msec, 199 +/- 14 msec, and 189 +/- 13 msec, respectively, during right ventricular (RV) pacing (P < 0.05). Posterior epicardial mapping (n = 4) showed that the APD(90) was significantly (P < 0.05) shorter than QT interval and DCaT(90) during pinacidil infusion. The results of the transmural mapping studies (n = 4) showed that the QT interval during RV pacing was not different than the DCaT(90) in the epicardium, midmyocardium, and endocardium, but was significantly (P < 0.01) longer than the APD(90) in epicardium, midmyocardium, and endocardium, respectively. There was a good correlation between the DCaT(90) and QT interval at baseline (r = 0.92, P < 0.0001) and during pinacidil infusion (r = 0.74, P < 0.0001).

CONCLUSION

We conclude that K(ATP) channel opening shortened APD but not the QT interval. Because Ca(i) did not return to diastolic level at the end of action potential, it may have created a heterogeneous membrane potential distribution that determined the QT interval.

QTc interval in patients with changing edematous states: implications on interpreting repeat QTc interval measurements in patients with anasarca of varying etiology and those undergoing hemodialysis

Associations have been described among weight, amplitude of QRS complexes, and QRS duration (QRSd) in patients with anasarca (AN), and changes in the amplitude of the QRS complexes, QRSd, and QTc after hemodialysis (HD) and in patients with heart failure with associated peripheral edema congestive heart failure. The objective of this study was to evaluate the hypothesis that changes in QTc in patients with AN and after HD are at least partially apparent, due to changing edematous states, and not totally due to altered electrophysiology. QTc was measured in patients with AN on admission, at peak weight (N = 28), and at their subsequent lowest weight (N = 12), in 28 control patients without change in weight during hospitalization, and in one patient before and after 26 HD sessions. In the patients with AN, the QTc was 451 +/- 36 ms on admission and dropped to 423 +/- 46 ms at peak weight (P = 0.005). QTc was 421 +/- 44 ms at peak weight and raised to 434 +/- 30 at subsequent lowest weight (P = 0.32). In the controls, QTc on admission and at discharge were 435 +/- 34 and 428 +/- 23 ms, correspondingly (P = 0.18). QTc increased from 472 +/- 18 ms before to 489 +/- 36 ms after HD (P = 0.017). Alterations in QTc in AN, or HD suggest that the changes in the QTc may be partially only apparent, and due to the electrocardiogram machine-based measurement of the attenuated/augmented QRST complexes resulting from fluid shifts.

Effect of coronary artery bypass grafting and aneurysmectomy on QT dispersion in moderate or severe left ventricular dysfunction

BACKGROUND

The aim of the study was to evaluate the effect that coronary artery bypass grafting (CABG) and aneurysmectomy in the same session have on QT dispersion (QTd) in moderate or severe left ventricular dysfunction.

METHODS

Forty-four patients underwent QT interval analyses before and 1 month after aneurysmectomy and CABG. QT interval and QTd were corrected for heart rate using the square root formula of Bazett (QTCB), the cubic root formula of Fridericia (QTCF), and the linear formula of Sagie et al (QT CS ).

RESULTS

The mean pre- and postsurgery QTd results were 65.29 +/- 29.25 and 51.76 +/- 18.49 milliseconds, respectively; the corresponding findings for QT CF were 68.06 +/- 31.26 and 55.16 +/- 24.56 milliseconds; and the corresponding findings for QT CS were 66.53 +/- 32.22 and 51.10 +/- 18.29 milliseconds. With these 3 methods, the postoperative findings were significantly lower than the preoperative findings ( P < .05 for all). In contrast, the opposite was true with the QT CB method (preoperative 71.1 +/- 65.80 vs postoperative 76.43 +/- 7.96 milliseconds, P < .05).

CONCLUSION

The study showed that based on the methods of Fridericia (QT CF ) and Sagie et al (QT CS ), QT intervals are significantly decreased after CABG and aneurysmectomy.

Effects of Cardiac Resynchronization Therapy on Ventricular Repolarization in Patients with Congestive Heart Failure

INTRODUCTION

Biventricular pacing has been shown to improve the clinical status of patients with congestive heart failure, but little is known about its influence on ventricular repolarization. The aim of our study was to evaluate the effect of biventricular pacing on ECG markers of ventricular repolarization in patients with congestive heart failure.

METHODS AND RESULTS

Twenty-five patients with congestive heart failure, sinus rhythm (SR), and complete LBBB (6 females; age 61 +/- 8 years; NYHA class II-III; echocardiographic ejection fraction 21 +/- 5%; QRS > or = 130 ms) underwent permanent biventricular DDDR pacemaker implantation. A high-resolution 65-lead body-surface ECG recording was performed at baseline and during right-, left-, and biventricular pacing, and the total 65-lead root mean square curve of the QRST complex and the interlead QT dispersion were assessed. The QRS duration was increased during right (RV)- and left ventricular (LV) pacing (127 +/- 26% and 117 +/- 40%; P < 0.05), as compared to SR (100%) and biventricular pacing (93 +/- 16%; ns). The QTc interval was increased during RV and LV pacing (112 +/- 12% and 114 +/- 14%; P < 0.05) as compared to SR (100%) or biventricular pacing (99 +/- 12%). There was no effect on JT interval during all pacing modes. The T(peak-end) interval was increased during right (120 +/- 34%; P < 0.01) and LV pacing (113 +/- 29%; P < 0.05) but decreased during biventricular pacing (81 +/- 19%; P < 0.01). A similar effect was found for the T(peak-end) integral and the T(peak) amplitude. QT dispersion was increased during right ventricular (129 +/- 16 ms; P < 0.05) and decreased during biventricular pacing (90 +/- 12 ms; P < 0.01), as compared to SR (114 +/- 22 ms).

CONCLUSIONS

Using a high-resolution surface ECG, biventricular pacing resulted in a significant reduction of ECG markers of ventricular dispersion of repolarization.

Prolonged Repolarization After Ventricular Assist Device Support Is Associated With Arrhythmias in Humans With Congestive Heart Failure

BACKGROUND

Recent observations indicate that the QTc interval often increases in the early postoperative period (<1 week) after mechanical unloading of severely failing hearts with a left ventricular assist device (LVAD). The present study examined whether early changes in ventricular repolarization after LVAD placement are associated with ventricular arrhythmias.

METHODS AND RESULTS

An electrocardiogram was obtained within 4 days before LVAD placement, <12 hours after LVAD placement, and weekly thereafter. Patient records were reviewed for documented ventricular tachycardia (VT) or ventricular fibrillation (VF) for 1 week preoperatively and the first 2 weeks postoperatively. Differences in QTc interval between patients with and without VT were evaluated. Ten of 17 patients enrolled (59%) had VT or VF after LVAD placement. Of these, 4 required therapeutic intervention because of clinical instability or symptoms. The change in the QTc (DeltaQTc) between the preoperative and immediate postoperative period was significantly different among patients with VT/VF compared with patients without VT/VF (+23 ms vs. -68 ms, P < .001).

CONCLUSION

The early period after initiation of LVAD support of the failing human heart is associated with a relatively high incidence of significant ventricular arrhythmias after LVAD placement. Beyond the impact of myocardial inflammation and wound healing occurring after all LVAD implants, early postoperative increases in the QTc interval after cardiac unloading appear to predispose to ventricular arrhythmias.

Repolarization changes induced by air pollution in ischemic heart disease patients

Epidemiologic studies report associations between particulate air pollution and cardiovascular morbidity and mortality, but the underlying pathophysiologic mechanisms are still unclear. We tested the hypothesis that patients with preexisting coronary heart disease experience changes in the repolarization parameters in association with rising concentrations of air pollution. A prospective panel study was conducted in Erfurt, East Germany, with 12 repeated electrocardiogram (ECG) recordings in 56 males with ischemic heart disease. Hourly particulate and gaseous air pollution and meteorologic data were acquired. The following ECG parameters reflecting myocardial substrate and vulnerability were measured: QT duration, T-wave amplitude, T-wave complexity, and variability of T-wave complexity. Fixed effect regression analysis was used adjusting for subject, trend, weekday, and meteorology. The analysis showed a significant increase in QT duration in response to exposure to organic carbon; a significant decrease in T-wave amplitude with exposure to ultrafine, accumulation mode, and PM2.5 particles (particles < 2.5 microm in aerodynamic diameter); and a corresponding significant increase of T-wave complexity in association with PM2.5 particles for the 24 hr before ECG recordings. Variability of T-wave complexity showed a significant increase with organic and elemental carbon in the same time interval. This study provides evidence suggesting an immediate effect of air pollution on repolarization duration, morphology, and variability representing myocardial substrate and vulnerability, key factors in the mechanisms of cardiac death.

QT interval abnormalities are often present at diagnosis in diabetes and are better predictors of cardiac death than ankle brachial pressure index and autonomic function tests

OBJECTIVES

To study serial measures of maximum QT interval corrected for heart rate (QTc) and QT dispersion (QTD) and their association with cardiac mortality patients with non-insulin dependent diabetes and to compare QT abnormalities with other mortality predictors (ankle brachial pressure index (ABPI) and autonomic function tests) in their ability to predict cardiac death.

SETTING

Teaching hospital.

METHODS AND PATIENTS

QT interval analysis, heart rate (RR) variation in response to deep breathing and standing, and ABPI were analysed in 192 patients with non-insulin dependent diabetes. Cardiac death was the primary end point.

RESULTS

Mean (SD) follow up was 12.7 (3.2) years (range 1.2-17.1 years). There were 48 deaths, of which 26 were cardiac. QTc and QTD were individually significant predictors of cardiac mortality throughout the follow up period (p < 0.001). The predictability of QT parameters was superior to the predictability of ABPI and RR interval analysis. Temporal changes in QT parameters showed that the mean absolute QT parameter was a significant predictor of cardiac death (p < 0.001), whereas an intraindividual change in QT parameter over time was not predictive.

CONCLUSION

QT abnormalities seem to exist at the point of diagnosis of diabetes and do not appear to change between then and the subsequent cardiac death. Furthermore, the analysis of QT interval is superior to ABPI and the RR interval in identifying diabetic patients at high risk of cardiac death.

Drug-induced QT dispersion: does it predict the risk of torsade de pointes?

Drug-induced delay in ventricular repolarization and proarrhythmias have attracted considerable regulatory attention. The measure of delayed ventricular repolarization most frequently used clinically is the ability of the new chemical entity (NCE) to prolong the QTc interval on surface electrocardiogram. Before they can be approved, new chemical entities with systemic bioavailability require characterization for their potential to prolong the QTc interval. Inevitably, QTc interval prolongation has come to be recognized as a surrogate marker of the risk of torsade de pointes (TdP)--a unique form of potentially fatal polymorphic ventricular tachycardia. Although it is the best and the simplest clinical measure that is available at present, QTc interval is not a reliable surrogate of TdP. Intramyocardial dispersion of repolarization appears to play a more important role both in electrical stability of the ventricles and in arrhythmogenesis. The potential importance of myocardial dispersion of refractoriness in arrhythmogenesis has led to a number of attempts to assess it from the surface electrocardiogram. This review summarizes the evidence for and against the predictive value of one of these attempts-measurement of the so-called QT dispersion. Although the concept of QT dispersion is the best known and most widely investigated, it has also proved to be the least successful in predicting the risks of drug-induced TdP.

Relation of dose of carvedilol to reduction in QT dispersion in patients with mild to moderate heart failure secondary to ischemic or to idiopathic dilated cardiomyopathy

Carvedilol has been shown to improve survival and morbidity in patients with heart failure. It has been demonstrated that carvedilol use is associated with dose-dependent reduction in QT dispersion (QTd) independent of the cause of heart failure, suggesting that reduction in QTd may be a mechanism by which carvedilol improves outcomes in heart failure.

Hypertensive Stress Increases Dispersion of Repolarization

Several electrocardiographic indices for repolarization heterogeneity have been proposed previously. The behavior of these indices under two different stressors at the same heart rate (i.e., normotensive gravitational stress, and hypertensive isometric stress) was studied. ECG and blood pressure were recorded in 56 healthy men during rest (sitting with horizontal legs), hypertensive stress (performing handgrip), and normotensive stress (sitting with lowered legs). During both stressors, heart rates differed <10% in 41 subjects, who constituted the final study group. Heart rate increased from 63 +/- 9 beats/min at rest to 71 +/- 11 beats/min during normotensive, and to 71 +/- 10 beats/min during hypertensive stress (P < 0.001). Systolic blood pressure was 122 +/- 15 mmHg at rest and 121 +/- 15 mmHg during normotensive stress, and increased to 151 +/- 17 mmHg during hypertensive stress (P < 0.001). The QT interval was larger during hypertensive (405 +/- 27) than during normotensive stress (389 +/- 26, P < 0.001). QT dispersion did not differ significantly between the two stressors. The mean interval between the apex and the end of the T wave (Tapex-Tend) of the mid-precordial leads was larger during hypertensive (121 +/- 17 ms) than during normotensive stress (116 +/- 15 ms, P < 0.001). The singular value decomposition T wave index was larger during hypertensive (0.144 +/- 0.071) than during normotensive stress (0.089 +/- 0.053, P < 0.001). Most indices of repolarization heterogeneity were larger during hypertensive stress than during normotensive stress. Hypertensive stressors are associated with arrhythmogeneity in vulnerable hearts. This may in part be explained by the induction of repolarization heterogeneity by hypertensive stress.

Principal Component Analysis of the T Wave in Patients with Chest Pain and Conduction Disturbances

There is a need for markers reflecting the increased risk in patients with conduction disturbances. Conduction disturbances presumably cause inhomogeneous repolarization that may create an arrhythmogenic substrate. In patients with normal conduction, parameters derived from principal components analysis (PCA) of the T wave contain prognostic information. The nondipolar PCA components are assumed to reflect repolarization inhomogeneity. This study examined the PCA parameters in relation to conduction disturbances. PCA was performed on continuously recorded 12-lead ECGs in 800 patients with chest pain and nondiagnostic ECG on admission. The patients with conduction disturbance on admission were classified into separate groups and related to comparison groups without conduction disturbance recruited from the same series. For each patient, the dipolar and nondipolar components were quantified by medians of the ratio of the two largest eigenvalues (S2/S1 Median), the residue that summarizes the eigenvalues S4-S8 (TWRabsMedian) and the ratio of this residue to the total power of the T wave (TWRrelMedian). The parameters were assessed with respect to common clinical and ECG parameters, discharge diagnosis, and total mortality during a 35-month follow-up. TWRabsMedian increased with increasing conduction disturbance. In 135 patients with conduction disturbances, ROC curves for TWRabsMedian as indicator of mortality exhibited areas under a curve of 0.66, 0.65, and 0.56 at 6-month, 24-month, and 35-month follow-up. Conduction disturbances were associated with increased nondipolar PCA component and, thus, with increased repolarization inhomogeneity. The nondipolar PCA component contained a moderate amount of prognostic information not present in a simple ECG diagnosis of a conduction disturbance.

QT dispersion, QT maximum and risk of cardiac death in the Caerphilly Heart Study

BACKGROUND

It has been postulated that increased inter-lead differences in QT interval (QT dispersion) and the maximum QT interval (QTmax), in the standard 12-lead electrocardiogram (ECG), may be associated with an increased risk of cardiac death. The aims of this study were to assess the relationship between QT dispersion and QTmax, corrected and uncorrected for heart rate, and the risk of cardiac death.

DESIGN

Nested case-control study within the Caerphilly prospective cohort study.

METHODS

We studied 2512 men who participated in phase 1 of the Caerphilly study between 1979 and 1983. After a mean follow up of 7.1 years, 218 men had died from coronary heart disease and these men were compared with 218 age-matched controls.

RESULTS

Data are presented on 422 patients with ECG suitable for analysis, 207 cases and 215 controls. Four trained observers measured the QT intervals and the reliability of each observer was estimated using repeat measurements on a randomly chosen sub-sample of ECGs. Median corrected QT dispersion and corrected QTmax were significantly higher in cases than in controls (51.9 versus 47.7 ms [P=0.01] and 430 versus 421 ms [P<0.001] respectively). In univariate analyses by quartiles of corrected QT dispersion and corrected QTmax, increased risk was largely confined to the upper quartile of the distribution with these subjects having twice the risk of those in the lower quartile [odds ratio (OR) 2.14, 95% confidence interval (CI) 1.2-3.7 and 2.56 (95% CI 1.5-4.5) respectively]. In logistic regression analysis, adjusted for age, smoking, body mass index, hypertension, history of myocardial infarction and ECG Minnesota code, we observed an increased risk in the upper quartile of the corrected QT dispersion relative to the other three quartiles combined [adjusted OR=1.74 (P=0.03)]. The magnitude of this association was increased in analyses based on the data from the most reliable observers. The association between corrected QTmax and cardiac death was attenuated in multivariate analysis. The findings in relation to both uncorrected QT dispersion and uncorrected QTmax were similar, i.e., consistent with a significant independent effect of QT dispersion but not QTmax for cardiac death in multivariate analysis.

CONCLUSION

The data suggest that QT dispersion is an independent predictor of cardiac death provided it can be measured with sufficient reliability. The association is non-linear with increased risk largely confined to the upper quartile of the distribution. The QT maximum is not an independent predictor of cardiac death.

QT dispersion correlates to myocardial viability assessed by dobutamine stress echocardiography in patients with severely depressed left ventricular function due to coronary artery disease

BACKGROUND

QT dispersion is prolonged in numerous cardiac diseases, representing a general repolarization abnormality.

AIM

To evaluate the influence of viable myocardium on QT dispersion in patients with severely depressed left ventricular (LV) function due to coronary artery disease.

METHODS AND RESULTS

103 patients with ischemic cardiomyopathy (LV ejection fraction [EF]: 25+/-6%) were studied. Patients underwent 12-lead electrocardiography to assess QT dispersion, and two-dimensional echocardiography to identify segmental dysfunction. Dobutamine stress echocardiography (DSE) was then performed to detect residual viability. Resting echo demonstrated 1260 dysfunctional segments; of these, 476 (38%) were viable. Substantial viability (> or =4 viable segments on DSE) was found in 62 (60%) patients. QT dispersion was lower in these patients, than in patients without viability (55+/-17 ms vs. 65+/-22 ms, P=0.012). Viable segments negatively correlated to QT dispersion (r=-0.333, P=0.001). In contrast, there was no correlation between LVEF and QT dispersion (r=-0.001, P=NS).

CONCLUSIONS

There is a negative correlation between QT dispersion and the number of viable segments assessed by DSE. Patients with severely depressed LV function and a low QT dispersion probably have a substantial amount of viable tissue. Conversely, when QT dispersion is high, the likelihood of substantial viability is reduced.

Corrected QT Dispersion and Cardiac Sympathetic Function in Patients With Obstructive Sleep Apnea-Hypopnea Syndrome

STUDY OBJECTIVES

Hypoxemia increases corrected QT dispersion (QTcD), which is the difference between the maximum and minimum QT intervals and is a strong risk factor for cardiovascular mortality. The aim of this study was to investigate the QTcD in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), and the relationship between the QTcD and (123)I-metaiodobenzylguanidine (MIBG) cardiac imaging, which reflects cardiac sympathetic activity.

SETTING

A university hospital.

PATIENTS

Forty-eight OSAHS patients without cardiac diseases (mean [+/- SD] age, 45.9 +/- 10.8 years; apnea-hypopnea index [AHI] 51.9 +/- 18.5 events per hour) who underwent polysomnography before treatment and on the first night of nasal continuous positive airway pressure (nCPAP) treatment.

METHODS

Before and after nCPAP treatment was started, we measured the QTcD with computer software, before, during, and after sleep, as well as the washout rate of the MIBG administered for cardiac imaging. As a control, QTcD was also measured in the morning from 26 healthy subjects.

RESULTS

Before treatment, the mean QTcD during sleep (65.0 +/- 14.6 ms) was greater than that before sleep (57.0 +/- 13.5 ms; p < 0.0001). Meanwhile, after 1 night of nCPAP therapy, the QTcD during sleep (50.6 +/- 11.4 ms) decreased from that before treatment (p < 0.0001) and was smaller than the QTcD before sleep (56.2 +/- 13.3 ms; p = 0.003). Before treatment, the QTcD during sleep correlated with the AHI (r = 0.38; p = 0.009) and the percentage of time that SaO(2) was < 90% (SaO(2) < 90% time) [r = 0.34; p = 0.018]. The QTcD did not correlate with the body mass index or the washout rate of MIBG. However, the washout rate of MIBG correlated with the AHI and the SaO(2) < 90% time.

CONCLUSIONS

Nocturnal QTcD is increased in OSAHS patients but is decreased by nCPAP therapy independently of cardiac sympathetic function.

Increased QT dispersion in patients with alcoholic pancreatitis

OBJECTIVES

Increased dispersion of the QT interval has been proposed to be a novel marker for increased risk of ventricular arrhythmia and sudden cardiac death. This study examined whether QT dispersion is affected in patients with alcoholic pancreatitis.

METHODS

We measured the QT interval, corrected QT interval, activation recovery interval, activation time, recovery time, and their respective dispersions in 3 age- and gender-matched groups: patients with alcoholic pancreatitis [age, 58.9 +/- 11.8 years; male/female (M/F), 33/3], patients with alcohol dependence (age, 59.3 +/- 8.9 years; M/F, 33/4), and a healthy control group (age, 55.8 +/- 8.8 years; M/F, 33/3).

RESULTS

The QT dispersions in patients with alcoholic pancreatitis (62.4 +/- 19.9 milliseconds; P < 0.001) or alcohol dependence (58.2 +/- 19.6 milliseconds; P < 0.001) were significantly greater than in the control group (41.4 +/- 13.3 milliseconds). Similarly, the corrected QT dispersions in patients with alcoholic pancreatitis (68.5 +/- 22.8 milliseconds; P < 0.001) or alcohol dependence (65.3 +/- 23.6 milliseconds; P < 0.001) were significantly greater than in the control group (42.8 +/- 13.2 milliseconds). Both QT dispersion and QTc dispersion were longer in patients with alcoholic pancreatitis than those with alcohol dependence (P = 0.011 and P = 0.039, respectively). Simple linear regression analysis of the relationship between the RR and QT intervals revealed that the regression lines for patients with alcoholic pancreatitis and alcohol dependence were almost parallel. However, the slope of the regression line for the control group was significantly greater (P < 0.05) than for the other 2 lines.

CONCLUSION

The findings demonstrate increased QT and QTc dispersions in patients with either alcoholic pancreatitis or alcohol dependence. The QT dispersion and QTc dispersion were longer in patients with alcoholic pancreatitis than those with alcohol dependence.

Heart rate-corrected QT interval prolongation predicts risk of coronary heart disease in black and white middle-aged men and women: the ARIC study

OBJECTIVES

We aimed to study the predictive value of heart rate-corrected QT interval (QTc) for incident coronary heart disease (CHD) and cardiovascular disease (CVD) mortality in the black and white general population, and to validate various QT measurements.

BACKGROUND

QTc prolongation is associated with higher risk of mortality in cardiac patients and in the general population. Little is known about the association with incident CHD. No previous studies included black populations.

METHODS

We studied the predictive value of QTc prolongation in a prospective population study of 14,548 black and white men and women, age 45 to 64 year. QT was determined by the NOVACODE program in the digital electrocardiogram recorded at baseline.

RESULTS

In quintiles of QTc, cardiovascular risk profile deteriorated with longer QTc, and risk of CHD and CVD mortality increased. The high risk in the upper quintile was mostly explained by the 10% with the longest QTc. The age-, gender-, and race-adjusted hazard ratios for CVD mortality and CHD in subjects with the longest 10% relative to the other 90% of the gender-specific QTc distribution were 5.13 (95% confidence interval 3.80 to 6.94) and 2.14 (95% confidence interval 1.71 to 2.69), respectively. The increased risk was partly, but not completely, attributable to other risk factors or the presence of chronic disease. The association was stronger in black than in white subjects. Manual- and machine-coded QT intervals were highly correlated, and the method of rate correction did not affect the observed associations.

CONCLUSIONS

Long QTc is associated with increased risk of CHD and CVD mortality in black and white healthy men and women.

Preconditioning reduces QTc value in patients with first non-ST-segment elevation myocardial infarction (NSTEMI)

BACKGROUND

Preinfarction angina (PA) consists a strong clinical correlate to ischemic preconditioning (PC) and seems to occur in a bimodal time course. The aim of the study is to evaluate the impact of both forms of PC on QTc value representing myocardial electric stability, in patients with a first NSTEMI.

METHODS

Forty-eight patients, with first NSTEMI and poor or no collateral development were enrolled in the study. QTc at admission and discharge were recorded. All patients had comparable admission QTc values and were divided into three groups according to the absence or presence and exact timing of preinfarction angina. The first group consisted of 20 patients who did not report PA (PA-, representing no PC effect); the second group of 12 patients with reported PA within 12 hours prior to admission (12h PA+, representing the classic form of PC); and the third group of 16 patients reporting PA within 12 to 48 hours prior to admission (48-hour PA+, representing the delayed form of PC). The primary outcome was determined as the effect of PA on QTc value at discharge.

RESULTS

Discharge QTc values were significantly reduced in both (PA+) groups compared to (PA-) group (412 +/- 50 vs. 455 +/- 53 ms, p = 0.015 and 417 +/- 29 vs. 455 +/- 53 ms, P = 0.033, respectively). Both groups of (PA+) patients compared to (PA-) patients suffered no arrhythmic events during their hospitalization (0/12 vs. 6/20, P = 0.04 and 0/16 vs. 6/20, P = 0.02).

CONCLUSIONS

Both forms of preconditioning, similarly and significantly reduce QTc value at discharge in patients experiencing a first NSTEMI, suggesting possible protection from future arrhythmic events.

Computerized QT dispersion measurement and cardiovascular mortality in male veterans

We examined the prognostic value of computerized measurements of QT dispersion in 37,579 male veterans. The results of our study showed that QT dispersion is a poor independent predictor of cardiovascular mortality.

Electrocardiographic repolarization complexity and abnormality predict all-cause and cardiovascular mortality in diabetes: the strong heart study

Type 2 diabetes is associated with increased risk of cardiovascular (CV) and all-cause mortality. Although electrocardiographic measures of repolarization abnormality and complexity stratify risk in the general population, their prognostic value in diabetes has not been well characterized. Digital electrocardiogram (ECG) readings were acquired for 994 American Indians with type 2 diabetes. ST segment depression (STD) >/=50 micro V and rate-corrected QT interval (QTc) >460 ms were examined as measures of repolarization abnormality. The principal component analysis (PCA) of the ratio of the second to first eigenvalues of the T-wave vector (PCA ratio) (>32.0% in women and >24.6% in men) was examined as a measure of repolarization complexity on the ECG. After a mean follow-up of 4.7 +/- 1.0 years, there were 56 CV deaths and 155 deaths from all causes. In univariate analyses, STD, QTc, and the PCA ratio predicted CV and all-cause mortality. After multivariate adjustment for age, sex, and other risk factors, STD (hazard ratio 3.68, 95% CI 1.70-7.96) and PCA ratio (2.61, 1.33-5.13) remained predictive of CV mortality and both STD (2.36, 1.38-4.02) and QTc (2.03, 1.32-3.12) predicted all-cause mortality. Computerized ECG measures of repolarization abnormality and complexity predict CV and all-cause mortality in type 2 diabetes, supporting their use to identify high-risk individuals with diabetes.

Correlation between dispersion of repolarization (QT dispersion) and ventricular ectopic beat frequency in patients with acute myocardial infarction: a marker for risk of arrhythmogenesis?

BACKGROUND

QT dispersion (QTd) has evoked a lot of interest in recent years as regards the basic concept of dispersion of repolarization, which it is supposed to reflect on a surface ECG, as being a marker or substrate for arrhythmogenesis. QTd has been shown to be high in patients with ventricular fibrillation and tachycardia. But there is still some debate about its possible role as a marker or substrate for arrhythmogenesis. We studied whether it has any correlation with simple benign ventricular ectopic beats (VEB) after acute myocardial infarction.

STUDY

We studied four different dispersion parameters (QTd, QTcd, JTcd, AQTd) on 2 different days after AMI and also obtained a 24-h ambulatory ECG on the 2nd day after admission in 64 out of a total of 90 patients. Patients were divided into five groups based on VEB frequency/h on a 24-h ambulatory ECG.

RESULTS

We found a gradual increase in dispersion parameters across the five groups with increasing frequency of VEB. A significant difference was noticed between group 1 (VEB 0.0-0.9/h) and group V (>30/h) on the day of admission: QTd 88.8+/-28.5 versus 123.3+/-23.4, P<0.02; QTcd 100.5+/-27.6 versus 160.3+/-30.7, P<0.01; JTcd 95.5+/-31.0 versus 160.4+/-30.9, P<0.01; AQTd 29.6+/-8.2 versus 48.6+/-13.7, P<0.01. We also noticed a significant positive correlation between VEB frequency and dispersion parameters on both days.

CONCLUSION

We hypothesize that with increasing dispersion of repolarization the chances or the frequency of ventricular arrhythmias increase. Our findings also point to a definite role of QTd as an arrhythmogenic marker or substrate.

Relation between QT dispersion and myocardial viability in ischemic cardiomyopathy

The aim of this study was to evaluate the relation between QT dispersion and myocardial viability as assessed by single-photon emission computed tomography. The study population included 97 consecutive patients with severely impaired left ventricular function secondary to chronic coronary artery disease. Patients with a low QT dispersion had a substantial amount of viable myocardium, whereas patients with a high QT dispersion had predominantly nonviable scar tissue.

QTc interval prolongation is a predictor of future strokes in patients with type 2 diabetes mellitus

BACKGROUND AND PURPOSE

QTc interval prolongation is a predictor of cardiovascular morbidity and mortality in general populations and in patients with diabetes. The aim of this study was to investigate the predictors of stroke in patients with type 2 diabetes, with particular emphasis on the independent role of QT interval parameters.

METHODS

We carried out a long-term follow-up study with 471 type 2 diabetics. Several clinical, laboratory, ECG, and echocardiographic variables were recorded at baseline. Predictive factors for stroke were evaluated by Kaplan-Meier estimation of survival curves and by univariate and multivariate Cox survival analyses.

RESULTS

After a median follow-up of 57 months (range, 2 to 84 months), 40 incident strokes were observed. QTc interval prolongation (>or=470 ms1/2) was an independent predictor of stroke, with adjusted hazard ratios ranging from 2.2 to 2.9 (95% confidence intervals, 1.1 to 6.0). Other independent factors associated with stroke were older age; the presence of cerebrovascular disease at baseline; increased 24-hour proteinuria, serum triglycerides, and left ventricular mass; and decreased high-density lipoprotein cholesterol. Excluding patients with previous cerebrovascular disease from the analysis did not change the results significantly.

CONCLUSIONS

QTc interval prolongation is a predictor of future stroke in patients with type 2 diabetes. Intervention studies are needed to assess whether this factor could be modified.

Multivariate associates of QT interval parameters in diabetic patients with arterial hypertension: importance of left ventricular mass and geometric patterns

The aim of the study was to assess the determinants of increased QT interval parameters in diabetic patients with arterial hypertension and, in particular, the strength of their relationships to echocardiographically derived left ventricular mass (LVM) and geometric patterns. In a cross-sectional study with 289 hypertensive type 2 diabetic outpatients, maximal QT and QTc (heart rate-corrected) intervals, and QT, QTc, and number-of-leads-adjusted QT interval dispersions were manually measured from standard baseline 12-lead ECGs. Electrocardiographic criteria for left ventricular hypertrophy (LVH) were either Sokolow-Lyon or Cornell sex-specific voltages. LVM and geometric patterns were determined by 2D echocardiography. Statistical analyses involved bivariate tests (Mann-Whitney, chi2, Spearman's correlation coefficients, ANOVA and receiver-operating-characteristic (ROC) curve analyses) and multivariate tests (multiple linear and logistic regressions). QT dispersion measurements showed significant correlations with echocardiographic LVM (r=0.26-0.27). ROC curves demonstrated a poor isolated predictive performance of all QT parameters for detection of LVH (areas under curve: 0.58-0.59), comparable to that of electrocardiographic voltage criteria. Only patients with concentric hypertrophy had significantly increased QT dispersion (QTd) when compared to those with normal geometries (64.24+/-21.09 vs 53.20+/-15.35, P<0.05). In multivariate analyses, both electrocardiographic and echocardiographic LVH were independent predictors of increased QTd, as well as only QTd and gender were determinants of LVM. In conclusion, increased QT interval dispersion is associated with LVM and concentric hypertrophy geometric pattern in diabetic hypertensive patients, although in isolation neither QTd nor any QT parameter presents enough predictive performance to be recommended as screening procedures for detection of LVH.

Prognostic value of QT interval parameters for mortality risk stratification in Chagas' disease: results of a long-term follow-up study

BACKGROUND

QT interval parameters are potential prognostic markers of arrhythmogenicity risk and cardiovascular mortality and have never been evaluated in Chagas' disease.

METHODS AND RESULTS

Outpatients (738) in the chronic phase of Chagas' disease were enrolled in a long-term follow-up study. Maximal heart rate-corrected QT (QTc) and T-wave peak-to-end (TpTe) intervals and QRS, QT, JT, QTapex, and TpTe dispersions and variation coefficients were measured manually and calculated from 12-lead ECGs obtained on admission. Clinical, radiological, and 2-dimensional echocardiographic data were also recorded. Primary end points were all-cause, Chagas' disease-related, and sudden cardiac mortalities. During a follow-up of 58+/-39 months, 62 patients died, 54 of Chagas' disease-related causes and 40 suddenly. Multivariate Cox survival analysis revealed that the QT-interval dispersion (QTd) (hazard ratio, 1.45; 95% confidence interval, 1.29 to 1.63; P<0.001, for 10-ms increments) and left ventricular (LV) end-systolic dimension (hazard ratio, 1.36; 95% confidence interval, 1.21 to 1.53; P<0.001, for 5-mm increments) were the strongest independent predictors for all end points. The maximum QTc interval (QTcmax) could substitute for QTd with a worse predictive performance. Other predictors were heart rate, presence of pathological Q waves, frequent premature ventricular contractions (PVCs), and isolated left anterior fascicular block (LAFB) on the ECGs. Kaplan-Meier survival curves demonstrated that a QTd > or =65 ms or a QTcmax > or =465 ms1/2 discriminated the 2 groups with significantly different prognoses.

CONCLUSIONS

Electrocardiographic QTd and echocardiographic LV end-systolic dimension were the most important mortality predictors in patients with Chagas' disease. Heart rate, the presence on ECG of pathological Q waves, frequent PVCs, and isolated LAFB refined the mortality risk stratification.

Ziprasidone in the management of schizophrenia : the QT interval issue in context

Ziprasidone is a new atypical antipsychotic recently marketed in a number of countries. Its main advantage over other atypical and typical drugs is its low propensity for causing weight gain. However, ziprasidone has been shown to prolong to some extent the cardiac corrected QT (QTc) interval, a property shared by a number of other antipsychotics. Prolongation of the QTc interval is linked to the ventricular tachyarrhythmia torsade de pointes, which is occasionally fatal, although the precise association between QTc changes and risk of sudden cardiac death has not been determined. QTc prolongation is certainly linked in some way to an increased risk of sudden cardiac death, and this may explain the recent, somewhat preliminary, reports of increased risk associated with use of some antipsychotics. Ziprasidone prolongs QTc to a moderate degree, though to a greater extent than quetiapine, risperidone, olanzapine and haloperidol. There is also preliminary evidence that ziprasidone blocks the delayed potassium rectifier channel in cardiac cells. Because of this, and despite the fact that no increased risk of arrhythmia or sudden death has been demonstrated for ziprasidone, some caution is required. Ziprasidone should be avoided in patients with some types of cardiac disease and with uncontrolled electrolyte disturbance. Coprescription of ziprasidone with other drugs that prolong the QT interval should be avoided where possible. When cross-tapering with other antipsychotics, care should be taken to avoid high total load of antipsychotics, and cross-tapering with drugs known to prolong QT interval at normal clinical doses should be avoided. Under most clinical circumstances, however, ziprasidone may be safely used without ECG monitoring or other special precautions. Its effect on QT interval and possible effect on risk of arrhythmia should be balanced with the observation that the drug has a more favourable effect on bodyweight and glucose homeostasis (and so perhaps cardiac risk) than many other antipsychotics.

Electrocardiographic ventricular repolarization parameters in chronic Chagas' disease as predictors of asymptomatic left ventricular systolic dysfunction

Electrocardiographic repolarization parameters are potential markers of arrhythmogenic risk and have not been evaluated in Chagas' disease. The aim of this report was to investigate their associations with LV systolic function assessed by two-dimensional echocardiography. In a cross-sectional study involving 738 adult outpatients in the chronic phase of Chagas' disease, maximal QTc and T wave peak-to-end (TpTe) intervals, and QT, QTapex (QTa), IT and TpTe interval dispersions, and variation coefficients were measured and calculated from 12-lead standard ECGs. Clinical, radiological, ECG, and echocardiographic data were recorded. In bivariate statistical analysis, all repolarization parameters were significantly increased in patients with moderate or severe LV systolic dysfunction, and these patients showed more clinical, radiologic, and ECG abnormalities. Receiver operating characteristic curve analysis demonstrated that isolatedly QTd had the best predictive performance for LV dysfunction, with an 80% specificity and 67% sensitivity for values >60 ms in the subgroup of chagasic patients with abnormal ECGs and no heart failure. Multivariate logistic regression selected, as the best predictive model for LV dysfunction in this subgroup of patients, the presence of cardiomegaly on chest X ray (OR 14.06, 95% CI, 5.54-35.71), QTd >60 ms (OR 9.35, 95% CI, 4.01-21.81), male gender (OR 7.70, 95% CI, 2.98-19.91) and the presence of frequent premature ventricular contractions (PVCs) on ECG (OR 4.06, 95% CI, 1.65-9.97). This model showed 90% specificity and 71% sensitivity. In conclusion, QTd was associated to LV systolic function and could be used to predict asymptomatic dysfunction in chronic Chagas' disease. The presence of cardiomegaly, frequent PVCs, and male sex refined LV function stratification in these patients.

Investigation of the potential of clozapine to cause torsade de pointes

Antipsychotics are frequently associated with QTc interval prolongation, a proposed marker for vulnerability to fatal ventricular arrhythmias, e.g. torsade de pointes (TdP). Little has been published on this topic in relation to clozapine. The objectives of this review were to: (i) calculate the frequency of QTc interval prolongation, T-wave abnormalities, TdP, ventricular tachycardia/fibrillation and sudden unexplained death in patients treated with clozapine and thioridazine from clinical trial and post-marketing reports; (ii) to compare these data with published findings for haloperidol, risperidone, olanzapine, sertindole and ziprasidone; and (iii) to correlate these clinical data with results from preclinical tests presently considered to be of predictive value for a compound's potential to cause QTc interval prolongation and TdP. A review of the global Novartis databases for clozapine and thioridazine and a Medline/Internet search for information on these cardiac events and for preclinical effects on the human ether-a-go-go related gene channels, action potential duration, and QT interval changes produced by the selected antipsychotics were performed. The clozapine database (2.8 million patient-years spanning 27 years) demonstrated that at therapeutic doses all but three reports of QTc interval prolongation and both of TdP were confounded by relevant co-medication/comorbidity. The literature review revealed that all antipsychotics considered except clozapine induced TdP and/or QTc interval prolongation at therapeutic doses. Preclinical in vitro tests appear to overestimate the risk of clozapine, haloperidol and risperidone to prolong QTc interval in patients and underestimate such a risk for sertindole and ziprasidone. Extrapolation of in vitro results to clinical events requires qualified interpretation.

Long QTc predicts future cardiac death in stroke survivors

OBJECTIVES

To test the hypothesis that the QTc of any lead of the ECG predicts death after stroke, and to determine which lead of the ECG carries the greatest risk of cardiac death when its QTc is measured.

DESIGN

Standard 12 lead ECGs were analysed by one observer who was blind to patient outcome.

SETTING

A major teaching hospital in Scotland.

PATIENTS

404 stroke survivors were studied at approximately one year after the cerebrovascular event and followed for up to 6.3 years.

OUTCOME MEASURES

Death from any cause and cardiac mortality.

RESULTS

The QTc measured from any lead of the ECG (except aVR) was associated with death from any cause. A prolonged QTc in limb lead III and chest lead V6 carried the highest relative risk of cardiac death (a 3.1-fold incease). After adjusting for overt ischaemic heart disease, pulse pressure, glucose, and cholesterol, a prolonged QTc in lead V6 was associated with a relative risk of cardiac death of 2.8 (95% confidence interval (CI) 1.1 to 7.3) (p = 0.028) and of death from all causes of 2.9 (95% CI 1.6 to 5.3) (p < 0.001). If the QTc in V6 exceeded 480 ms, then the specificity of predicting cardiac death within five years after the stroke was 94%.

CONCLUSIONS

Although treatment of the conventional modifiable risk factors is important, stroke survivors with a prolonged QTc in lead V6 are still at a high risk of cardiac death and may need more intensive investigations and treatments than are currently routine practice.

Antipsychotics and QT prolongation

OBJECTIVE

To evaluate literature relating to cardiac QT prolongation and the use of antipsychotic drugs.

METHOD

Literature searches of EMBASE, Medline, PsychLIT were performed in December 2001 and reference sections of retrieved papers scrutinized for further relevant reports.

RESULTS

The Cardiac QTc interval is difficult to measure precisely or accurately but appears to be a useful predictor of risk of dysrhythmia (specifically torsade de pointes) and sudden death. It is less clear that drug-induced QTc prolongation gives rise to similar risks but data are emerging, linking antipsychotic use to increased cardiac mortality. Many antipsychotics have been clearly associated with QTc prolongation. Methodological considerations arguably preclude assuming that any antipsychotic is free of the risk of QTc prolongation and dysrhythmia.

CONCLUSION

Available data do not allow assessment of relative or absolute risk of dysrhythmia or sudden death engendered by antipsychotics but caution is advised. Risk of dysrhythmia can very probably be reduced by careful prescribing of antipsychotics in low doses in simple drug regimens which avoid metabolic interactions. Electrocardiographic monitoring may also help to reduce risk but review by specialist cardiologist may be necessary.

QT dispersion has no prognostic value in patients with symptomatic heart failure: an ELITE II substudy

This study prospectively investigated 3,118 standard 12-lead ECGs recorded in 1,804 patients, who participated in the Losartan Heart Failure Survival Study--ELITE II clinical trial. After exclusion of patients with rhythms other than sinus, or atrioventricular block, or poor quality ECGs, 986 (703 men, mean age 71 +/- 7 years) with baseline ECGs were retained, of whom 615 patients had follow-up ECGs 4 months after randomization. QT intervals were manually measured with a digitizing board. Heart rate, QRS duration, maximum QT and JT intervals, QT and JT dispersion (the interval ranges across all measurable ECG leads) were analyzed. In the overall population, there were 140 (14%) deaths from all causes, including 119 (12%) cardiac and 59 (6%) sudden deaths during a follow-up of 540 +/- 153 days. The mean heart rate was significantly faster in nonsurvivors than in survivors (77 +/- 16 vs 74 +/- 14 beats/min, P = 0.006), and in patients who died of cardiac death (76 +/- 16 beats/min, P = 0.04 vs survivors). Mean QRS duration was significantly longer in nonsurvivors (107 +/- 25 ms), and in the subgroups who died of cardiac (107 +/- 24 ms) or sudden death (112 +/- 23 ms) than in survivors (99 +/- 24 ms, P < 0.01 for all). The maximum and corrected (QTc) QT intervals were similar for nonsurvivors, regardless of cause of death, and in survivors (P = NS for all comparisons). Significantly shorter maximum and corrected (JTc) JT intervals were observed in victims of any mode of death compared to survivors (P < 0.05 for all). There was no significant difference in QT or JT dispersion between patients with any mode of death and survivors (P > 0.1 for all). Neither losartan nor captopril significantly modified QT or JT dispersion. In conclusion, increased QT dispersion is not associated with increased mortality in patients with heart failure, and is not suitable to examine drug efficacy in these patients.

Seasonal variability of QT dispersion in healthy young males

BACKGROUND

There are few data related to the seasonal influences on the QT dispersion.

METHODS

We analyzed the effects of seasons on QT dispersion in a large group of healthy young males. We studied the seasonal variability of QT dispersion in 523 healthy male subjects aged 22 +/- 4 years (ranging from 20 to 26). Four seasonal 12-lead resting electrocardiograms (ECGs) recorded at double amplitude were performed at 25 mm/s at intervals of 3 months. Subsequent ECGs were recorded within 1 hour of the reference winter recording. QT dispersion was defined as the difference between the longest and the shortest mean QT intervals.

RESULTS

There was a significant seasonal variation in QT dispersion (P = 0.001), with the largest QT dispersion in winter (71 +/- 18 ms) and the smallest one in spring (43 +/- 19).

CONCLUSION

There exists a significant seasonal variation in QT dispersion of healthy subjects and such variability should be taken into consideration in the evaluation process of QT dispersion.

Quantitative assessment of electrocardiographic strain predicts increased left ventricular mass: the Strong Heart Study

OBJECTIVES

This study was designed to examine the relation of computer-measured ST depression (STdep) in the lateral precordial leads to the presence of left ventricular hypertrophy (LVH).

BACKGROUND

Qualitative abnormalities of repolarization in the lateral precordial leads of the electrocardiogram, as manifested by the strain pattern of T-wave inversion and STdep, are markers for LVH and adverse prognosis. However, the independent relationship of increased left ventricular (LV) mass to quantitative measures of STdep in these leads remains unclear.

METHODS

Electrocardiograms and echocardiograms were examined in the second Strong Heart Study examination in 1,595 American Indian participants without evident coronary disease. The absolute magnitude of ST segment deviation above or below isoelectric baseline was measured by computer in leads V(5) and V(6), and participants were grouped according to gender-specific quartiles of maximal STdep. Left ventricular hypertrophy was defined by indexed LV mass >49.2 g/m(2.7) in men and >46.7 g/m(2.7) in women.

RESULTS

Increasing STdep was associated with older age, greater pulse pressure, serum fibrinogen levels and urinary albumin/creatinine ratios, and with stepwise increases in LV mass (145 +/- 28 vs. 150 +/- 33 vs. 156 +/- 36 vs. 164 +/- 43 g, p < 0.001), indexed LV mass (38.2 +/- 7.7 vs. 39.3 +/- 8.7 vs. 40.5 +/- 9.4 vs. 44.0 +/- 11.0 g/m(2.7), p < 0.001), and prevalence of LVH (11.6 vs. 19.1 vs. 21.5 vs. 31.2%, p < 0.001). After controlling for clinical differences, increasing STdep remained strongly associated with increased prevalence of LVH (p = 0.0001).

CONCLUSIONS

In the absence of evidence of coronary disease, increasing STdep in the lateral precordial leads is associated with increasing LV mass and increased prevalence of anatomic LVH.

QT dispersion measured by an automatic continuous method early in patients admitted for chest pain

BACKGROUND

There is a need for risk markers in patients with acute chest pain. QT dispersion (QTd) is a prognostic marker in several groups of patients. A problem with the manual measurement of QTd is operator dependency. This can be avoided by using an automatic method. We investigated QTd, derived from multiple automatic measurements, as a risk marker in a population with chest pain.

METHODS

In 548 patients admitted to the coronary care unit for chest pain and nondiagnostic ECG, 12-lead ECG recordings were collected each minute during the initial 17 h. From recordings with > or =10 valid leads, mean QTd (QTdMean), QTd in the first satisfactory recording and estimates of variability of QTd were computed and correlated to outcome.

RESULTS

In the group with QTdMean > or =40 ms (n=277), 10 patients died during the initial 30 days; one patient died in the group with QTdMean <40 ms (n=271) (P=0.07). During follow-up (median 6 months), 19 vs. five patients died in each group (P=0.03). The figures for the triple endpoint death/myocardial infarction/revascularisation were 52 vs. 27 events during the initial 30 days (P=0.018) and 76 vs. 41 events during follow-up (P=0.003). QTd in the first recording did not predict new cardiac events.

CONCLUSIONS

QTd measured as the mean value of multiple recordings was found to be a powerful marker for cardiac events during follow-up. It was superior to the analysis of QTd in a single ECG. It can be used for the selection of low-risk patients, but was not effective in identifying high-risk patients.

QT interval and QT dispersion increase in the elderly during laparoscopic cholecystectomy: a preliminary study

PURPOSE

To compare the influence of a longer duration of intraperitoneal CO2 insufflation with head-up tilt on electrocardiogram indices during laparoscopic cholecystectomy between elderly and younger patients.

METHODS

Twelve elderly and 12 younger patients were studied. In all patients, intraperitoneal CO2 insufflation was performed for more than 150 min in the head-up position. RR interval, QT interval, the rate-corrected QT (QTc) interval, QT dispersion (QTD) and the rate-corrected QTD (QTcD) were measured.

RESULTS

The QT interval and the QTc interval increased significantly from 120 to 150 min after CO2 insufflation in the elderly. The QTD and QTcD increased significantly during CO2 insufflation in both groups. Those were significantly greater in the elderly than in younger patients from 120 to 150 min after CO2 insufflation.

CONCLUSION

Longer duration of CO2 insufflation with head-up tilt is associated with a prolongation of the QT interval and the QTD in elderly patients. The clinical significance of these findings remains to be determined.

n-3 fatty acids and the risk of sudden cardiac death

Sudden cardiac death (SCD) is a major cause of mortality in Western countries. Furthermore, SCD is often the first manifestation of coronary artery disease, making it difficult to prevent. Heart rate variability (HRV), which can be determined by extended recording of the heart rate by 24-h Holter monitoring, has been shown to be one of the best predictors of the risk of SCD. There is increasing evidence from animal experiments and clinical trials in humans that n-3 fatty acids reduce the risk of SCD. We have studied the effect of n-3 fatty acids on HRV and present data clearly showing that n-3 fatty acids increase HRV. This adds further to the hypothesis that an increased intake of n-3 fatty acids may reduce the risk of SCD.

QT-RR relationship in healthy subjects exhibits substantial intersubject variability and high intrasubject stability

Recently, it was demonstrated that the QT-RR relationship pattern varies significantly among healthy individuals. We compared the intra- and interindividual variations of the QT-RR relationship. Twenty-four-hour 12-lead digital electrocardiograms (ECGs; SEER MC, GE Marquette; 10-s ECG recorded every 30 s) were obtained at baseline and after 24 h, 1 wk, and 1 mo in 75 healthy subjects (42 women, 33 men, age 27.9 +/- 9.6 vs. 26.8 +/- 7.5 yr, P = not significant). QT interval was measured automatically in each ECG by six different algorithms, and the mean of the six measurements was analyzed. In each recording of each individual, QT-RR relationship was assessed by 10 different regression models including linear (QT = beta + alpha x RR) and parabolic (QT = beta x RR(alpha)) models. Standard deviations (SDs) of regression parameters alpha and beta of consecutive recordings of each individual were compared with SD of the individual means. Intrasubject stability and interindividual variability were further tested by ANOVA. With all models, intraindividual SDs of the regression parameters were highly significantly smaller than SD of individual means (P < 10(-5)-10(-9)). The intrasubject stability was further confirmed by ANOVA (P < 10(-19)-10(-30)). The QT-RR relationship exhibits substantial intersubject variability as well as a high intrasubject stability. This has practical implications for a precise estimation of the heart rate-corrected QT interval in which optimized subject-specific rate correction formulas should be used.

Cholinergic stimulation with pyridostigmine reduces the QTc interval in coronary artery disease

Parasympathetic dysfunction is an independent risk factor in patients with coronary artery disease; thus, cholinergic stimulation is a potential therapeutic measure that may be protective by acting on ventricular repolarization. The purpose of the present study was to determine the effects of pyridostigmine bromide (PYR), a reversible anticholinesterase agent, on the electrocardiographic variables, particularly QTc interval, in patients with stable coronary artery disease. In a randomized double-blind crossover placebo-controlled study, simultaneous 12-lead electrocardiographic tracings were obtained at rest from 10 patients with exercise-induced myocardial ischemia before and 2 h after the oral administration of 45 mg PYR or placebo. PYR increased the RR intervals (pre: 921 +/- 27 ms vs post: 1127 +/- 37 ms; P<0.01) and, in contrast with placebo, decreased the QTc interval (pre: 401 +/- 3 ms vs post: 382 +/- 3 ms; P<0.01). No other electrocardiographic variables were modified (PR segment, QT interval, QT and QTc dispersions). Cholinergic stimulation with PYR caused bradycardia and reduced the QTc interval without important side effects in patients with coronary disease. These effects, if confirmed in studies over longer periods of administration, may suggest a cardioprotection by cholinergic stimulation with PYR.